1. Field of the Invention
The present invention relates to a portable power working machine such as a chain saw, an engine cutter or a hedge trimmer, etc, wherein a small air-cooled internal combustion engine is mounted thereon as a power source for driving a working member of the working machine. In particular, the present invention relates to the portable power working machine which is capable of effectively preventing icing from generating at a intake system of the internal combustion engine especially in cold seasons.
2. Description of the Related Art
A portable power working machine such as a chain saw is generally constructed such that a small air-cooled two-stroke gasoline internal combustion engine such as a small air-cooled internal combustion engine having a displacement of about 25-100 mL is mounted in a main housing as a power source for driving the working member thereof such as a saw chain, and that a cooling fan driven by the internal combustion engine is disposed on one side of the main housing of the engine so as to permit part of the air that has been sucked into the main housing by this cooling fan to be introduced, via an air cleaner and carburetor into the internal combustion engine.
In this portable power working machine as described above, there is usually encountered with a trouble of so-called icing in cold seasons wherein the water component in the sucked outer air is caused to freeze at the components such as carburetor constituting the air intake system of the internal combustion engine; thereby giving rise to the malfunctioning of the internal combustion engine.
As for the countermeasure for the prevention of the icing, there has been considered to utilize the air that has been once sucked into the main housing by means of the cooling fan for cooling the internal combustion engine, i.e. to introduce part of the air (warm air) that has been heated by the internal combustion engine into the air cleaner and carburetor to thereby warm the air cleaner and the carburetor.
If it is desired to employ the aforementioned countermeasure wherein the air once employed for cooling the internal combustion engine and warmed up is to be introduced into the air intake system, there is a matter that should be especially taken into account particularly if the portable working machine is any one of a chain saw, an engine cutter and a hedge trimmer, etc. Namely, dust such as relatively large saw dusts, cut powder or sandy dust would be inevitably generated during the operation thereof, so that these dusts are permitted to be sucked together with air into the main housing by the cooling fan. If the air (warmed air) containing a large quantity of such dust is permitted to introduce into the air intake system of the internal combustion engine, these dusts are likely to be adhered onto the air cleaner (the filter portion thereof), thereby giving rise to the generation of clogging of the filter at an early stage of operation. As a result, the malfunction of the internal combustion engine or the deterioration in performance of the internal combustion engine would be caused due to an insufficiency of air that can be introduced into the internal combustion engine.
Furthermore, it is desirable that the air to be introduced as a medium for preventing the icing into the air intake system of the internal combustion engine should be as high in temperature as possible. However, when the internal combustion engine is operated in warm seasons where there is little possibility of generating the icing, the introduction of warmed air into the air intake system of the internal combustion engine would become unfavorable on the contrary, inviting the malfunction and the deterioration of the internal combustion engine. Therefore, it may become necessary to provide the intake system with means for switching the introduction and non-introduction of warm air to be used for the prevention of the icing.
The present invention has been achieved in view of the aforementioned problems and hence, an object of the present invention is to provide a portable working machine which is capable of rationally and effectively preventing the generation of the icing that may be caused to generate at the air intake system of a small air-cooled internal combustion engine to be mounted thereon as a power source for driving the working component thereof without giving rise to early clogging of an air cleaner, to the malfunction of the internal combustion engine, or to the deterioration of performance.
With a view to realize the aforementioned object, there is provided, according to the present invention, a portable power working machine, which comprises a small air-cooled internal combustion engine mounted inside a main housing; a cooling fan disposed on one side of the main housing and designed to be driven by means of said internal combustion engine; a carburetor coupled to an upper portion of an intake port of said internal combustion engine; a clean air chamber disposed on an upstream side of said carburetor; an air cleaner cover coupled to said clean air chamber; a warm air introducing passageway for introducing, through a region adjacent to said intake port, part of air which has been inhaled by said cooling fan for cooling said internal combustion engine into said air cleaner cover, and a shutter for externally opening or closing said warm air introducing passageway as desired.
According to a preferable embodiment of the present invention, the internal combustion engine is mounted in such a manner that a cylinder thereof is disposed lateral with said intake port being disposed upward and a head portion thereof being disposed rearward.
In a preferable embodiment, a laterally L-shaped top handle is disposed over an upper surface of said main housing, and a rear upright portion of said top handle is provided with said carburetor, said clean air chamber, and a downstream portion of said warm air introducing passageway.
The warm air introducing passageway is preferably disposed on the other side of said main housing which is opposite to said one side of said main housing as well as on the other side of said rear upright portion which is opposite to said one side of said main housing, so that air warmed by the internal combustion engine is permitted to pass, through said other sides of said carburetor and of said clean air chamber, to an upper portion of an external air chamber formed inside said air cleaner cover.
In another preferable embodiment, an inlet port for said warm air introducing passageway is provided adjacent to said intake port disposed at a cooling air guide cover enclosing a cylinder portion of said internal combustion engine, and said shutter is disposed to open and close said inlet port.
The air cleaner cover should preferably be formed of a cap-like configuration, an interior of which is communicated, through a filter member functioning as a partitioning wall, with said clean air chamber, this air cleaner cover being detachably secured to a rear end portion of said rear upright portion.
As for the portable power working machine to which the present invention can be applied, a typical example thereof would be a chain saw which is provided, on the aforementioned other side of the main housing, with a saw chain set constituted by a saw chain and a guide bar, thereby enabling to discharge a large quantity of dust such as saw dust during the operation thereof.
According to preferable embodiments of the portable power working machine which have been constructed according to the present invention, in cold seasons where the aforementioned phenomenon of icing may be permitted to occur, the shutter for opening and closing the inlet port of the warm air introducing passageway provided close to the intake port at the cooling air guide cover enclosing the cylinder portion of the internal combustion engine is externally operated so as to open the shutter. As a result, part of the air that has been sucked by means of the cooling fan for cooling the internal combustion engine (i.e. the air (warm air) that has been warmed by the internal combustion engine) is permitted to enter from the inlet port located close to the intake port into the warm air introducing passageway and then, introduced into the air cleaner cover, in which dust that may be included in the air is removed at the filter member disposed inside the air cleaner cover. Thereafter, the resultant air is permitted to pass through the clean air chamber and the carburetor and introduced through the intake port. As explained above, since the air intake system constituted by the air cleaner and the carburetor, etc. can be warmed up by the warmed air, the generation of icing can be rationally and effectively prevented.
In this case, since the air that has been introduced into the warm air introducing passageway from a region close to the intake port is heated higher than the air disposed at a region which is located below the warm air introducing passageway, it contains a reduced quantity of dust due to the effects of gravity and inertia, and the air intake system can be rapidly warmed up by the warmed air without giving rise to early clogging of the filter member disposed inside the air cleaner cover, to the malfunction of the internal combustion engine, or to the deterioration of performance.